Currently, impact type fastening tools, such as impact screwdrivers, generally perform a striking operation through use of continuous impacting motions. However, in some operating conditions, when a strike needs to be applied one more time after a screw is positioned flush with a surface of a workpiece or when pretension needs to be increased after a bolt is tightened, upon using an ordinary impact type tool, a user needs to control output and cut-off of the impact by controlling a trigger by himself, whereupon manual control of impact time usually damages the surface of the workpiece or causes damage by applying excessive pretension to the bolt due to error of the control time, which imposes very high requirements for the user's operation and causes trouble during operation.
With respect to the above problem, some solutions are proposed, for example, a motor is automatically stopped upon detecting the times of impact reaching a preset value; or the motor is stopped by using a sensor to detect and judge whether impact occurs and depending on whether an ON state and operation duration of a main switch exceeds a predetermined duration after the impact of the first time. However, these methods require precise detection and judgment of impact times or the impact of the first time, so an additional sensor needs to be positioned nearby an impact swing block to detect the swing block, thereby making the structure more complicated and causing the cost of the impact type fastening tool to be too high.